It is generally known to provide refrigeration devices (e.g. temperature controlled cases, refrigerated storage units, merchandisers, coolers, etc.) having a refrigeration system for circulating a refrigerant or coolant through one or more cooling elements within the case to maintain items (such as food products and the like) within a certain desirable temperature range. The temperature of the refrigerant circulated through the cooling element(s) is usually below 32 degrees F. When moisture in the air within the case contacts the surface of the cooling element (e.g. by forced or natural circulation) the moisture tends to freeze. Over time, a build-up of frost and/or ice accumulates on the surface of the cooling elements and tends to reduce the performance and the efficiency of the temperature controlled case. It is also generally known to provide defrost systems for removing frost and/or ice from the surfaces of the cooling element that accumulate during operation of the case in a cooling mode.
Such defrost systems typically involve at least one of three conventional methods. A first type of defrost system interrupts the cooling mode to stop circulation (or cooling) of a refrigerant for a sufficient period of time (e.g. “time-off” defrost) so that the temperature of the cooling element rises above the freezing point (i.e. 32 degrees F) and the accumulated frost and ice melt into a drain pan or the like for removal from case. However, such time-off defrost systems tend to permit the temperature of food products stored within the case to fluctuate to an extent that may lead to more rapid degradation of the food product. A second type of defrost system interrupts the cooling mode and energizes electric heating elements coupled to (or adjacent to) the cooling element for a sufficient period of time to melt the accumulated frost and ice for drainage from the case. However, such heating elements may increase thermal shock and stress to the cooling element material during defrosting and tends to add heat to the case. A third type of defrost system interrupts the cooling mode to circulate a heated fluid (such as hot refrigerant gas or warmed secondary coolant) through the cooling coil to melt accumulated frost and ice for drainage from the case. However, such hot gas or warmed coolant systems typically require additional components and controls that tend to increase the complexity of the case and also add heat to the case. Therefore, the typical defrost systems may tend to reduce the overall thermal performance of the case and may cause undesirable degrees of thermal shock and/or stress to components of the cooling system, and add heat to the case.
Accordingly, it would be desirable to provide a defrost system for a cooling element in a temperature controlled case that minimizes the duration of the defrost mode, so that temperature fluctuation of products within the case is minimized and thermal stress of the cooling element and addition of heat to the case is minimized. It would also be desirable to provide a defrost system that operates on an increased frequency to perform frequent, short-duration “mini-defrosts.” It would also be desirable to provide a defrost system that modulates the flow of refrigerant through the cooling element to increase the average temperature of the cooling element slightly above the freezing point (i.e. 32 degrees F) during the mini-defrosts. It would be further desirable to provide a defrost system that regulates a throttle device (such as a superheat valve) to modulate the flow of refrigerant during the mini-defrosts. It would also be desirable to control the frequency of the mini-defrosts in a time-based manner. It would be further desirable to control the frequency of the mini-defrosts in a demand-based manner.
Accordingly, it would be desirable to provide a defrost system for a temperature controlled case having any one or more of these or other desirable features.